1. Technical Field
The present invention relates to spreaders which are connectable to a single container in single lift operations and optionally to two containers connectable to the spreader in end facing relationship in twin lift operations. More specifically, the invention refers to a spreader wherein the concurrent displacements of locking means are synchronized in twin lift operations, without the need for a mechanical connection between associated locking means. In accordance herewith, the invention also relates to a method for synchronizing the concurrent displacements of inner and outer locking means in a spreader during twin lift operations.
2. Background and Prior Art
In the field of container handling in ports and freight yards, rising demands for efficiency and reduced loading/unloading times lead the development towards spreaders with capacity for the simultaneous lift of two 20-feet containers, while the capacity for single lift needs to be maintained. The spreaders adapted for single/twin operation conventionally are equipped with outer locking means carried in the ends of extendable beams telescopically supported in a main beam, while inner locking means are supported on the main beam and controllable between an operative position allowing twin lift, and a non-operative position allowing single lift operation. As used herein, the expression “twin lift operation” shall be understood as an operation wherein two containers are handled simultaneously by the spreader, while the containers are aligned with the end walls thereof facing each other. In twin lift operations, the distance between inner and outer locking means is adjustable and determined by the length of the container, or more precisely, by the center-to-center distance between connection holes in each corner of the container, the corner castings.
Additionally, in twin lift operations, there is a frequent need to adjust internally the distance between the two sets of locking means on the spreader with respect to a spacing between the two containers to be handled. Obviously, upon connecting, a synchronization of the relative position between inner and outer locking means in both sets of locking means is necessary for an accurate lowering into the corner castings of the container. Likewise, a synchronized displacement of outer and inner locking means is necessary in lifting/lowering movements while adjusting the spacing between the two containers in a length direction.
Synchronization is conventionally provided through a controllable mechanical connection connecting the inner locking means to the extendable beam, this way urging the inner locking means to move synchronously with the outer locking means in extension/retraction motion. The mechanical connection between outer locking means/extendable beam and inner locking means may be realized in the form of a latch that is hydraulically powered and controllable to engage a belt or chain drive which operates the extendable beams in extension/retraction movements. Other solutions may include a link member, eventually comprising a hydraulic cylinder, by which the inner locking means are connectable to the beam. Examples of prior art in this connection may be found in WO 03/099699 and WO 97/39973, for example.
Typically, the spreader's extendable beams are hydraulically powered in telescopic movements. While hydraulic power thus conventionally is present on the spreader for this purpose, also other moving elements on the spreader, such as the inner locking means and the controllable mechanical links for synchronization of motions, are conveniently operated through hydraulic power, as are the lowering and raising motions of the flipper arms and the lock/unlock rotation of the locking means' twist-locks.
However there is an increasing desire, not the least driven by environmental demands, to depart from the use of oil in ports and in freight yards as well. The implementation of environmentally clean power on spreaders includes the use of electricity and electric drive means. In the course of arriving at an all-electric spreader design, several issues need to be addressed in order to achieve reasonable power consumption and, consequently, reasonable dimensions and weight in motors and transmissions.